Brian Francis Yates

Hypervalent iodine(V) reagents such as 2-iodoxybenzoic acid (IBX) are widely used oxidants, yet their reactivity is highly sensitive to structural modification. Here, a dataset of 284 IBX derivatives was analysed using density functional theory and interpretable machine learning to quantify substituent effects on the key hypervalent twisting barrier. Non-linear models substantially outperformed linear regression, revealing important descriptor interactions. The dihedral angle Θ emerged as the dominant predictor of activation free energy, while electronic effects were less influential. Ortho substitution promotes twisting through steric distortion, and multiple substituents further enhance this effect through cooperative steric buttressing, providing quantitative structure–reactivity relationships overall.

In seminal work on the oxidation of Pt ^II (acac) ₂ to trans ‐Pt ^IV (acac) ₂ I ₂ (acac = [acetylacetonato‐ O , O ′] ⁻ ) by diiodine, Hopgood and coworkers proposed that coordination of diiodine to platinum(II) occurs forming a complex Pt ^II (acac) ₂ ( η ¹ ‐I ₂ ) with a linear “Pt‐I–I” motif and that this complex reacts with I ^• via a free‐radical chain reaction following photochemical initiation of I ^• from uncoordinated diiodine (Hopgood et al. 1973). We report a computational study of this fundamental mechanistic proposal, finding support for the kinetic evidence. The iodine doublet interacts initially with the π ‐system of an acac group via the central γ ‐carbon atom, [(I···acac)Pt(acac)( η ¹ ‐I ₂ )] ^• , followed by migration to the platinum center leading to formation of an intermediate trans ‐[IPt(acac) ₂ I···I] ^• in which the “Pt‐I···I” group is bent (104.2°), and the peripheral iodine atom is weakly interacting (I···I 3.395 Å). Subsequent migration of I ^• to the other acac ligand leads to formation of a C _γ ···I interaction in trans ‐[Pt(acac)(acac···I)I ₂ ] ^• and finally departure to continue propagation releasing the end‐product trans ‐Pt ^IV (acac) ₂ I ₂ . The reverse reaction occurs by photochemical initiation of I ^• allowing access to trans ‐[Pt(acac)(acac···I)I ₂ ] ^• . Both the oxidation and the reverse reaction compute as low energy processes, Δ G ^† ca . 7 and ca . 10 kcal mol ⁻¹ , respectively, consistent with rapid reactions observed experimentally.

Proton-coupled electron transfer (PCET) plays a central role in oxidative iodine chemistry. In this study, we show that 2-iodobenzoic acid (1) is readily oxidized by Oxone to generate the I(V) species IBX, while 2-iodo-1,3-benzenedicarboxylic acid (8) is only oxidized to the I(III) species iodosodilactone (12). Density functional theory (DFT) calculations reveal that the oxidation of both substrates follows an inner-sphere two-electron transfer (IS-2ET) mechanism, in which push-pull interactions facilitate the process. While the initial I(I)-to-I(III) step proceeds with comparable activation barriers for both 1 and 8, the subsequent I(III)-to-I(V) oxidation is significantly less favorable for 8, with a barrier of 44.9 kcal/mol compared to 24.7 kcal/mol for 1. For compound 1, oxidation proceeds via an I(III) intermediate, iodosobenzoic acid (IBA), bearing an OH ligand. We found that IBA is oxidized to IBX with a moderate activation barrier when the reaction proceeds via an inner-sphere proton-coupled two-electron transfer (IS-PC2ET), in which deprotonation of the OH group precedes two-electron transfer to Oxone. In contrast, compound 12 lacks an OH ligand and cannot undergo IS-PC2ET, rendering further oxidation inaccessible. These findings reveal a distinct subclass of PCET mechanisms and provide guiding principles for designing iodine-based oxidants capable of accessing the I(V) state under mild conditions.

The pincer complex (2‐Tol)Pt^II(NCN) (NCN = [2,6‐bis{(dimethylamino)methyl}phenyl‐N,C,N]⁻) reacts with diiodine via electrophilic cleavage to give Pt^II(NCN)I and 2‐tolyl iodide, together with oxidative addition to give cis‐(2‐Tol)Pt^IV(NCN)I₂ (van Koten et al. 1990). Herein, it is reported that density functional theory computation for benzene as solvent indicates electrophilic cleavage occurs on a singlet manifold, while oxidative addition occurs via a radical chain mechanism related to that demonstrated for the reaction of Pt(acac)₂ (acac = [acetylacetonate]⁻) with diiodine (Hopgood and Jenkins, 1973). For the radical process, time dependent density functional theory calculations indicate that initiation occurs from ArPt^II(NCN)(η¹‐I₂) (Ar = 2‐Tol, Ph) giving trans‐[ArPt^III(NCN)I]^• which isomerizes to cis‐[ArPt^III(NCN)I]^•, where these doublets are isoelectronic with stable [Ni^III(NCN)I₂]^•. In the propagation reaction, cis‐[ArPt^III(NCN)I]^• reacts with ArPt^II(NCN)(η¹‐I₂) to form bridging complexes based on the motif “[Ar(NCN)Pt–I···I–Pt(Ar)(NCN)I]^•” that undergo internal electron transfer to release cis‐ArPt^IV(NCN)I₂ and regenerate trans‐[ArPt^III(NCN)I]^•. In the oxidative addition process for ArPt^II(NCN), computation demonstrates the intimate role of ArPt^II(NCN)(η¹‐I₂). The preference for electrophilic cleavage over oxidative addition based upon involvement of “Pt(η¹‐I₂)” species on a singlet surface is consistent with the involvement of spectroscopically undetected but computationally confirmed “Pd(η¹‐I₂)” species in palladium catalysis (Musaev et al. 2015).

Density functional theory is used to explore the geometries and properties of 55 heterocyclic carbenes containing N, P, As, Sb, Bi, O, S, Se, Te and Po. Planar and non-planar structures have been systematically evaluated and a variety of measures (including Wiberg bond indices, orbital occupancies, HOMO–LUMO gaps, proton affinities, J( ¹³ C– ¹ H) coupling constants and isodesmic reaction energies) have been considered for all systems. The main conclusions are that the heavier heteroatoms can be effective π-donors towards the carbene carbon if planarity can be attained, and that the cost of attaining this planarity is actually quite low for the majority of the heterocyclic carbenes considered.

The 2-iodoxybenzoic acid (IBX)-controlled oxidative dearomatization of pyrroles occurs very slowly (or not all) in many organic solvents, including DMSO in which IBX is soluble. Interestingly, although IBX is only partially soluble in acetic acid, this solvent mediates the pyrrole oxidative dearomatization. With the aid of density functional theory (DFT) calculations, we have discovered a new mode of reactivity, termed the periodinane oxy-assisted (POA) oxidation mechanism, which explains this observation.

Density functional theory (DFT) has been used to investigate the mechanism of the experimentally efficient hydroalkylation of styrene with acetylacetone in the presence of a bismuth catalyst. It is shown that the mechanism is fundamentally different to that of the analogous gold-catalysed reaction, even though it leads to the same product. Whereas gold prefers to coordinate to the π-bond of the enol isomer of acetylacetone, bismuth coordinates to the two oxygens to form a chelated complex. Furthermore, the overall reaction with bismuth via the enol isomer of acetylacetone occurs with a much lower activation energy compared to the ketone isomer. In addition, several bismuth catalysts were considered and two of these were shown to have no activity. All of these results have been rationalised in terms of the strength of binding of the metal centres to the acetylacetone. The stronger the binding, the greater the acidity of a proton on acetylacetone, and thus the lower the activation energy for the protonation of styrene, which turns out to be the rate-determining step in the overall reaction. In this way, good agreement is obtained with all the experimental data. GRAPHICAL ABSTRACT